Revert "Use python 3 for utilities"

This reverts commit 76c6c50405c6cbb1d08bdd7b5d27c657fa5d38b6, which broke the obs builds. I'm really starting to get annoyed by ongoing python related breakage without ever fixing any bugs!

Change-Id: I4d76e897d4f746ff9ea4e06f2efc708a12cc2944
diff --git a/utils/conv_gen.py b/utils/conv_gen.py
index d2eda15..6b6b267 100644
--- a/utils/conv_gen.py
+++ b/utils/conv_gen.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/bin/python2
 
 mod_license = """
 /*